Method of forming firearm barrels



Dec. 24, 1946. G. A. WOODY METHOD OF FORMING FIREARM BARRELS Filed Sept. 22, 1945 Patented Dec. 24, 1946 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a method for drilling bores having a large ratio of length to diameter, particularly, the bore of firearm barrels.

In the manufacture of firearms, especially rifles and machine guns, ther is no more diihcult step than the initial drilling of the barrel bore. It is essential that such bore be straight and concentrically located with respect to the barrel blank. The straightness of the bore path depends largely upon the initial position assumed by the drill. If the drill makes its initial cut at only a very slight angle to the bore axis, then the end of the drilled hole, due to the large ratio of length of barrel to its diameter, will be so displaced from the axis of the barrel blank as to reduce the wall thickness on one side to a de gree rendering the blank unusable. The problem is further complicated by the fact that few if any barrel blanks are straight and straightening operations prior to drilling are costly and time expending.

For the foregoing reasons it has been the practice of all manufacturers of firearm barrels to employ a barrel blank of substantially greater diameter than necessary in order to provide sufficient stock to compensate for misalignment of the drilling. This procedure requires more metal to be used per barrel and increases the amount of metal to be removed by subsequent machining operations. Hence the benefits obtained by the use of forged barrel blanks are largely neutralized.

Accordingly, it is an object of this invention to provide a novel method for accurate drilling of bores havin large ratio of length to diameter.

It is a particular object of this invention to provide an improved method for drilling the bore of firearm barrels.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

1 is a front elevational view showing the barrel mounted in the barrel drilling machine which is partly in longitudinal section with the drill about to enter the squared end surface of the barrel blank.

Fig. 2 is a side elevational view of the barrel blank showing the bore drilled accurately along the axis of the barrel blank.

Fig. 3 is a detail view partly in longitudinal section of the end of a barrel blank showing the non-conformity of the centering hole with respect to the end of the drill.

Fig. 4 is a detail view of the cutting end of the single lip stationary barrel drill.

Fig. 5 is a longitudinal sectional view of the lathe used for turning the ends of a barrel blank showing a warped barrel blank mounted therein for such turning,

As is well known to those skilled in the art of firearm barrel manufacture, best results in drilling barrel bores are obtained by the use of a stationary single lip drill such as is shown in Fig. 4. Such a drill is generally held stationary and is fed into a rotating barrel blank. Prior to drilling thebarrel blanks, however, it is customary practice to center drill each end of the barrel blank so that such blank may be centrally located in the turning machine or lathe to prepare such blank for the drilling machine.

While it appears that such an arrangement should produce a satisfactorily drilled hole in the barrel blank, it has been observed that the shape of the end of such drill does not conform at all to the contour of the centering hole usually provided in the end of the barrel. This is clearly shown in Fig. 3. As a resultof the drill being fed into such an unnatural hole as well as a hole burnished and work hardened by previous turning operation the end of the drill is thereby forcibly deflected from one side to the other of the centering hole. It is this deflection of the drill that is believed to be the principal cause of the drill entering the barrel in a slightly noncentric or angularly displaced position with respect to the barrel axis. It is apparent also that should the drill when emerging at the opposite end fail to properly align with the centering hole,

it is liable to serious injury. I

In this improved method for drilling firearm barrels, the need for centering holes has been eliminated and accordingly one of the primary causes of drilling misaligned bores has been overcome.

- In the practice of this improved method. barrel blank i can be forged to an exterior shape as shown in Fig. 5 approximating the final shape of the finished barrel. The barrel blank 5 is then turned down slightly on a center drive lathe at each end 2 and 3 to provide a chamfered surface 4 on the end 2 and a cylindrical surface 3 on the other end. In such turning operation the barrel blank I should however be sup orted at two points A and B intermed ate the ends of the blank as shown in Fig. 5. The points A and Bare preferably located approximately one-third the distance of the barrel in from each end 2 and 3 respectively. The barrel blank I is then held securely at these two points in a suitable machine such as a center drive lathe and revolved so that the ends may be turned down as above described and the chamfered end faced off perpendicular to the axis of the blank in this position. The chamfer 4 is provided on the large end 2 of barrel blank I for a purpose to be described. The location of the oints A and B is an important factor in obtaining increased accuracy of location of the drill while drilling the bore as such location minimines the effect a warped barrel blank has on run out of the drill.

The barrel blank I with the trued up ends is then transferred to a barrel drilling machine 5. The barrel drilling machine 5 is a'conventional machine which need not be fully described to illustrate the novel features of this invention. There is, however, a modification of the head of such machine which is necessary to accomplish the drilling of the barrel blank without the use of centers.

There is inserted in the head So. of the drilling machine 5 a revolving center 6 constructed to receive and support the large diameter end 2 of barrel blank I. The revolving center 6 comprises a spring biased drill guide bushing I, a barrel guide bushing 8 and a pair of ball bearing races 9. The revolving center assembly 6 is inserted within a suitable cylindrical recess I B in the head So of barrel drilling machine 5. The ball hearing races 9 are inserted within the recess IE! and are suitably spaced and retained therein to support the barrel guide bushing 8. Barrel guide bushing 8 is a cylindrical member provided with an enlarged integral head portion II. The head II continues out of the recess I of drilling machine head a.

An axial hole I2 is provided in barrel guide bushing 8 through which is inserted the drill guide bushing 1. Axial hole I2 is counterbored to receive an enlarged integral head portion I3 of drill guide bushing I. A spring I4 surrounds the body portion of drill guide bushing I which acts against the head portion I3 of bushing I thereby tending to bias drill guide bushing I out of barrel guide bushing 8. The spring I4 while biasing bushing 1 outwardly also exerts counterforce against bushing 8 thereby tending to retain bushing 8 within recess ID.

A chamfered surface I5 conforming to chamfered surface 4 on the end 2 of barrel blank I is provided on the insideof head II of bushing 8 as shown in Fig. 1. A single-li drill I6 (Figs. 1

and 4) is supported within an axial hole I! in bushing I.

On the bed I8 of drilling machine 5 directly opposite the revolving center 6. and spaced approximately the length of a barrel blank therefrom a power driven collet or chuck 20 is mounted on a suitable bracket I9. The collet or chuck 20 is a conventional clamping member and is arranged to be tightened by a hand wheel 2I in the usual manner or by a chuck wrench. Collet or chuck 20 is conventionally mounted on a revolving spindle 22 mounted on the upper portion of bracket I9. The spindle is arranged to be driven at high speed as by a pulley 23 secured to the center. of spindle 22 which in turn is suitably driven by a belt 24 connected to a suitable power source (not shown).

The drilling of the bore of barrel blank I is usually started from the breech or large end thereof although of course it is readily apparent that drilling may be started from either end of the barrel blank as desired. The end 3 of blank I is first loosely inserted in collet or chuck 20 then the right end 2 of barrel blank I is placed into the chamfered interior I5 of the end of barrel guide bushing 8 and is forced against the drill guide bushing I compressing the biasing spring I 4. Bushing l is also forced into contact with the bottom of recess ID thereby providing an effective oil seal around drill I6 in the bottom of recess Ill. The chamfered surface 4 on the end 2 of barrel blank I fits snugly against the chamfered surface I5 on the front face of head II of bushing 8 thereby centering the barrel blank in the revolving center 6 and at the same time providing a good oil seal. The necessity for a good oil seal is quite evident in view of the fact that oil under relatively high pressure is forced through an oil hole 25 in drill I6 as shown in Figs. 1 and 4 for the purpose of lubricating the drill and clearing away such chips as are formed by the drilling operation. The chips are of course moved back along the groove SI] provided in the drill, together with the excess oil. The other end 3 of barrel blank I which had been previously inserted in collet 20 is tightened therein by the hand wheel 2|. Thus when power is applied to belt or drive 24, the barrel blank I will be revolved by spindle 22 about the axis of chamfered surface 4 and cylindrical surface 3. The drill I6 is likewise concentric about such axis.

Drilling of the barrel bore may then be accomplished in this set-up without the use of centers. The barrel blank I is rotated by spindle 22 and drill I 6 is advanced into the barrel blank for the drilling operation. Drill It can be fed into the work piece at any desired rate by hand or by the Well known feeding mechanisms of the drilling machine. (not shown). The single-lip drill It thus will cut its own center at the start of the drilling operation and continue throughout the length of the barrel. Furthermore, the absence of a centering hole on extreme end obviates breakage of the drill point. 'I have found that this feature greatly improved the accuracy of the drilling operation and minimizes the large spoilage of barrels encountered when such are drilled by the conventional centering method.

Furthermore, barrel blanks having appreciable warpage may be successfully drilled by this method. Referring to Fig. 5 wherein a common type of warped barrel blank I is illustrated, it is readily apparent that the supporting points A and B for the initial truing of the ends 2 and 3 of the barrel blank I produces a drilling axis 26 through the barrel blank which avoids points of excessive reduction of Wall thickness due to warpage better than any other axis and certainly better than the axis 27 on which the blank would be drilled if both ends were centered.

Thus it may be readily seen that by truing up the ends of the barrel as previously described and drilling the bore of such blank by permitting the drill to find its own center that a barrel blank of smaller exterior dimensions may be readily utilized as the tendency of the drill to walk away from the longitudinal axis of the barrel blank has been greatly reduced and therefore more accurate drilling with greatly reduced spoilage is readily obtained.

I claim:

That method of forming a firearm barrel from a rod-like blank having a longitudinal central axis, comprising, supporting said blank for rotarevolution only, and while so supporting said blank forming the bore of said barrel by axially translating a drill from one end of said blank along the axis determined by said formed surfaces 6 of revolution while rotating said blank.

GEORGE A. WOODY. 

